Title: 3D retina-RPE constructs for vision restoration in new rat retinal degeneration model In patients with advanced degenerative diseases, both retinal pigment epithelium (RPE) and photoreceptors are lost. If new cells can restore the function of the lost cells, a degenerating retina might be repaired and eyesight restored. Our team targets vision restoration by transplanting sheets of retinal progenitor and RPE cells derived from human embryonic stem cells (hESCs) to recipients that have lost photoreceptors and retinal pigment epithelium (RPE) cells. Transplants of freshly harvested sheets of retinal progenitor cells (delivered by a unique procedure and instrument) have shown to develop photoreceptors with normal morphology, synaptic connections with the host and to restore lost visual responses in several retinal degeneration models and in human patients. This cannot be achieved by injecting dissociated cells into the retina. Although other approaches exist, the majority are restricted to rescue of endogenous retinal cells of the recipient by a 'nursing' role of the implanted cells, an approach which does not restore lost function. The supply of fresh fetal-derived neuroblastic tissue is limited. Differentiation of hESCs into sheets of photoreceptor progenitors and RPE cells would create an unlimited tissue supply for clinical and research use. Several laboratories have recently developed procedures to differentiate pluripotent stem cells into optic vesicles and optic cup-like structures that develop retinal cell types with some degree of lamination. We want to use this approach for producing laminated retinal progenitor sheets with RPE for transplantation. Our team has developed 1) a protocol to derive early retinal progenitor tissue from hESC and 2) a new immunodeficient rodent model of retinal degeneration. Additional pre-clinical animal research is required to develop a therapeutically viable and sustainable supply of stem cell derived material. A three-year project is proposed to test the hypothesis that (1) hESC-derived photoreceptor progenitors, transplanted together with a hESC-derived RPE sheet to a new immunodeficient rat model of RD, will develop mature photoreceptor markers and integrate with the degenerating host retina; (2) hESC-derived retinal progenitors can restore visual responses in this rodent model to the same extent as transplants of fetal retina with RPE, as shown by optokinetic testing and electrophysiology. Transplantation of intact ESC-derived retinal progenitor layers with RPE in rats with retinal degeneration provides an excellent model to answer an important question for developing retinal therapies. Proof of concept will provide a new tissue source to restore and improve vision in patients with retinal diseases.